The transport of alpha-aminoisobutyric acid (AIB), alanine (ALA), and N-methylated AIB (N-MAIB) have been studied in the erythroblastic leukemic cell (EBL), reticulocyte (Ret), erythrocyte (RBC), and the chloroleukemic cell (CLC) of the Long Evans Rat. The mature RBC exhibits no Na-Dependent (Na-dep) transport; with final steady state distribution ratios (SSDR) reaching approximately 1. The Ret exhibits Na-dep transport with SSDR in the presence of Na approaching 3 for ALA, 2 for AIB, and 1.5 for N-MAIB. The Na-dep system accounts for 54 percent of the total flux. In the EBL, a model immature erythroid cell, the Na-dep flux is 80 percent of the total flux and SSDR for AIB was 4, ALA 6, and N-MAIB of 3. For the CLC, a model immature myeloid cell, flux was greater than that of the EBL and, final SSDR for AIB was 17, ALA 18, and N-MAIB 14. The EBL and the CLC exhibit Na-dep transport systems which need both the free amino and carboxyl groups. A second system which needs a free carboxyl group and a third system which requires an N-methylated group for maximum transport. Both of these cells also exhibit Na-independent transport. The flux of the CLC is greater than that of the EBL. In the erythroid series the Ret has a Na- dep system which requires the amino and carboxyl groups for transports, an N-methylated requiring transport site and Na-independence sites. It has lost the transport group which requires only the carboxyl group. In the RBC no Na-dep processes are exhibited (only Na-independent transport). Even though the two blast cells are essentially one cell division off of the stem cell their membrane transport systems are quite different. Within the erythroid series as the cell matures it loses the Na-dep transport systems, retaining only the Na-independent systems.